NiO/Ni Metal–Organic Framework Nanostructures for Asymmetric Supercapacitors

An electrode material with high performance as a key part is highly desirable for supercapacitors. Herein, NiO/Ni metal–organic framework (Ni-MOF) composites were successfully synthesized via the first preparation of NiO nanoflakes and then in situ formation of Ni-MOF over NiO. Particularly, the conversion degree of Ni-MOF from NiO was conveniently tuned by altering the amount of terephthalic acid added in the hydrothermal process. NiO/Ni-MOF-25 with 25% of the conversion ratio of NiO to Ni-MOF possessed superior electrochemical performance with a specific capacity of 163.4 mA h g–1 (1176.6 F g–1) at a current density of 1 A g–1, higher than Ni-MOF (79.3 mA h g–1) and NiO (79.8 mA h g–1). The boosted electrochemical performance of NiO/Ni-MOF-25 was attributed to its core-shell configuration, relatively high specific surface area, and enhanced electrical conductivity. The assembled NiO/Ni-MOF-25//activated carbon asymmetrical supercapacitor achieved a maximum energy density of 31.3 W h kg–1 at a power density of 374.2 W kg–1 and decent cyclic durability with 88.7% of incipient capacitance after 2000 cycles. Moreover, two asymmetric devices in series constructed 3 months ago could efficiently illuminate a green light-emitting diode (LED) lamp. This work offers a facile way to rationally design and synthesize composite electrode materials for powerful supercapacitors.